We intend to develop a permanent cell line from normal epithelial cells of the human colonic mucosa, in order to compre its properties with those of human colonic carcinoma cells. Two recently introduced techniques should allow us to obtain this goal; namely: 1) the use of tsA mutants of SV40 to obtain transformants that will revert to the untransformed phenotype when shifted to the temperature restrictive for the viral gene; and 2) the use of the manual microinjecion technique, with which cloned viral genes can be introduced into cells, regardless of the presence of virus receptors of the cell surface, and with a high efficiency of transformation. Once a permanent cell line of normal colonic mucosa cells is established, it will be possible to compare it to human colonic carcinoma cells in culture and, even more importantly, in co-cultures in terms of growth, resistance to chemotherapeutic agents, nutrient requirements, etc.